CVE-2023-42450 in Mastodon
Summary
by MITRE • 09/19/2023
Mastodon is a free, open-source social network server based on ActivityPub. Starting in version 4.2.0-beta1 and prior to version 4.2.0-rc2, by crafting specific input, attackers can inject arbitrary data into HTTP requests issued by Mastodon. This can be used to perform confused deputy attacks if the server configuration includes `ALLOWED_PRIVATE_ADDRESSES` to allow access to local exploitable services. Version 4.2.0-rc2 has a patch for the issue.
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Analysis
by VulDB Data Team • 10/13/2023
CVE-2023-42450 represents a critical vulnerability in Mastodon server software that enables attackers to inject arbitrary data into HTTP requests through carefully crafted input. This vulnerability exists in versions 4.2.0-beta1 through 4.2.0-rc1, where the application fails to properly sanitize user-supplied data before incorporating it into outgoing HTTP requests. The flaw allows malicious actors to manipulate the request parameters, potentially leading to unauthorized access to internal services that would normally be restricted from external access. This issue directly relates to CWE-94, which describes the injection of untrusted data into command or query constructs, and falls under the broader category of CWE-74, representing injection flaws in web applications. The vulnerability becomes particularly dangerous when combined with specific server configurations that include ALLOWED_PRIVATE_ADDRESSES, which explicitly permits access to local services that may be exploitable. When these conditions align, attackers can leverage the injection capability to perform confused deputy attacks, where the server acts as an unwitting intermediary in malicious activities. The confusion arises because the server trusts the injected data and forwards it to internal services that it would normally not communicate with directly, effectively bypassing security controls that were designed to protect against such access patterns. This vulnerability demonstrates a classic example of how insufficient input validation can create pathways for attackers to escalate privileges and access sensitive internal resources. The patched version 4.2.0-rc2 addresses this issue through proper sanitization of input data before it is incorporated into HTTP requests, ensuring that user-supplied values cannot be manipulated to influence the destination or content of outgoing communications. Organizations using Mastodon servers should immediately upgrade to the patched version and review their server configurations to ensure that ALLOWED_PRIVATE_ADDRESSES is properly restricted to only necessary internal services. The attack vector for this vulnerability aligns with techniques described in the MITRE ATT&CK framework under T1190 for exploitation of remote services and T1071.004 for application layer protocol usage, specifically targeting HTTP communications. Security teams should implement monitoring for unusual outbound HTTP requests and establish proper access controls to prevent unauthorized internal service access, as the vulnerability essentially creates a tunnel through which attackers can reach otherwise protected internal resources.